STEEL HAVING SUPER FINE FERRITE GRAIN AND METHOD FOR MANUFACTURING THE SAME

摘要

Steel having super fine ferrite grain and a method for manufacturing the same are provided to manufacture the super fine ferrite grain having a ferrite particle size of 50 to 100nm within 3mum around an intermediate material. A method of manufacturing steel having super fine ferrite grain includes a heat treatment process in which a heating temperature is 800 deg.c or more. However, the heating temperature should be 1200deg.c or less. Then, after the heating, the heating temperature is maintained for a certain time or less, for example, 120min or less. Then, the heating temperature is lowered with a cooling speed of 0.01 to 50deg.c/sec. When the cooling speed is lower than 0.01 deg.c/sec, a super fine tissue is enlarged, and when the cooling speed is higher than 50 deg.c/sec, the tissue becomes martensite.